1. Field of the Invention
This invention relates to a device and method for separating heavier and lighter fractions of a fluid sample. More particularly, this invention relates to a device and method for collecting and transporting fluid samples whereby the device and fluid sample are subjected to centrifugation in order to cause separation of the heavier fraction from the lighter fraction of the fluid sample.
2. Description of Related Art
Diagnostic tests may require separation of a patient""s whole blood sample into components, such as serum or plasma, the lighter phase component, and blood cells, the heavier phase component. Samples of whole blood are typically collected by venipuncture through a cannula or needle attached to a syringe or an evacuated collection tube. Separation of the blood into serum and blood cells is then accomplished by rotation of the syringe or tube in a centrifuge. Such arrangements use a barrier for moving into an area adjacent the two phases of the sample being separated in order to maintain the components separated for subsequent examination of the individual components.
A variety of devices have been used in collection and separation devices to divide the heavier and lighter phases of a fluid sample.
The most widely used device includes thixotropic gel material such as polyester or silicone gels. The present gel serum separation tubes require special manufacturing equipment to prepare the gel and to fill the tubes. Moreover, the shelf-life of the product is limited in that over time unbound resin may be released from the gel mass. This resin may have a specific gravity that is less than or equal to the separated serum and may float in the serum and may clog the measuring instruments such as the instrument probes used during the clinical examination of the sample collected in the tube. Such clogging can lead to considerable downtime for the instrument to remove the clog.
In addition, no commercially available gel is completely chemically inert to all analytes. If certain drugs are present in a blood sample when it is taken, there can be a chemical reaction at the gel interface.
Therefore, a need exists for a separator device that (i) is easily used to separate a blood sample; (ii) is independent of temperature during storage and shipping; (iii) is stable with radiation sterilization; (iv) employs the benefits of a thixotropic gel barrier yet avoids the many disadvantages of placing a gel in contact with the separated blood components; (v) minimizes cross contamination of the heavier and lighter phases of the sample; (vi) minimizes entrapment of the lower and higher density materials within the separator device; (vii) is able to move into position to form a barrier in less time than conventional methods and devices; (viii) is able to provide a clearer serum or plasma specimen with less cell contamination than conventional methods and devices; and (ix) can be used with standard sampling equipment.
The present invention is a method and assembly for separating a fluid sample into a higher specific gravity phase and a lower specific gravity phase. Desirably, the assembly of the present invention comprises a plurality of constituents. Preferably, the assembly comprises a container, such as a tube, a deformable container, such as a bag, and a flowable separation medium.
Most preferably, the deformable container is provided for positioning within a tube and includes a flowable fluid separation medium capable of maintaining separation of the separated fluid phases. The deformable container is deformably repositionable under centrifugation from a first condition permitting a fluid sample within the tube to a second condition establishing a physical separation between the separated fluid phases.
Preferably, the deformable container includes a flexible bag which is reconfigurable under centrifugation from a first condition to a second condition. The flowable fluid separation medium preferably includes a thixotropic fluid such as a gel having a specific gravity, which under centrifugation, becomes resident between the separated fluid sample phases. The flexible bag may be adheringly secured to the inner wall of the tube so as to provide for the deformable movement of the bag and the gel contained therein from a position adjacent the lower end of the tube to an intermediate position within the tube under centrifugation so as to establish residence of the gel in the bag between the separated fluid phases of the fluid sample. The flexible bag is preferably sealed with the gel completely contained therein.
The assembly of the present invention is advantageous over existing separation products that use gel. One advantage is that the assembly of the present invention will not interfere with analytes as compared to gels that may interfere with analytes. In particular, the assembly will not interfere with therapeutic drug monitoring analytes.
Another notable advantage of the present invention is that fluid specimens are not subjected to low density residuals such as unbound resins that are at times available in products that use gel.
Additionally, the assembly of the present invention does not require any additional steps or treatment by a medical practitioner whereby a blood or fluid sample is drawn in the conventional way, using standard sampling equipment.